Myopic corneal ring with central accommodating portion

ABSTRACT

A bio-compatible corneal ring for myopic correction and accommodation for presbyopia. The corneal ring is made from a bio-compatible material with a lens body having an inner and outer circular edge. The inner circular edge forms an opening in the lens body. The posterior surface of the lens body has a uniform radii of curvature between the inner and outer circular edges. The anterior surface has two radii of curvatures providing for correction of myopia. The first radii of curvature extends from near the outer circular edge to a junction point before the inner circular edge. The second radii of curvature extends from the junction point and continues to the inner circular edge. The inner and outer circular edges have a thickness of less than about 0.020 mm, but preferably are about 0.010 mm or less.

This application is a continuation of U.S. Ser. No. 10/610,000, filedJun. 30, 2003, which is a continuation of U.S. Ser. No. 10/053,178,filed Oct. 7, 2001, now U.S. Pat. No. 6,623,522, and claims prioritythereto.

FIELD OF THE INVENTION

The field of this invention relates to prosthetic implants designed tobe implanted in the cornea for modifying the cornea curvature andaltering the corneal refractive power for correcting myopia andaccommodating for presbyopia.

BACKGROUND OF THE INVENTION

It is well known that anomalies in the shape of the eye can be the causeof visual disorders. Normal vision occurs when light passes through andis refracted by the cornea, the lens, and other portions of the eye, andconverges at or near the retina.

In a myopic or near-sighted eye, the cornea is too steeply curved forthe length of the eye. This curvature causes light rays to converge at apoint before it reaches the retina. Distant objects, therefore, appearout-of-focus or blurry since the light rays are not in focus by the timethey reach the retina. Approximately one in four persons have myopicvision.

In persons who are older, a condition called presbyopia occurs in whichthere is a diminished power of accommodation of the natural lensresulting from the loss of elasticity of the lens. Ordinarily the eyemay vary its optical power by focusing the natural lens. However, withthe loss of lens elasticity, the eye muscles cannot bend or focus thelens needed for clear vision of near objects. Typically presbyopiabegins about the age of 40 and becomes significant after the age of 45.

Corrections for myopia and presbyopia have been attempted primarilythrough the use of prescriptive lenses in the form of glasses. Manyadults wear bifocals or trifocals to correct their vision to see clearlyat different distances. Generally, a bifocal lens is arranged such thatthe upper portion of the lens is used for distance vision and the lowerportion for near vision. For reading, a person looks through the lowerportion of the lens.

Additionally, available for the correction of myopia and presbyopia arehard, gas-permeable, and soft contact lenses. These contact lenses comein a variety of designs and provide bifocal correction. Also known formulti-vision correction are diffractive contact lenses where the surfaceof the lenses have invisible ridges molded into concentric circles.Generally, light passing through the lens is bent so that the wearer'snear and distant vision is corrected. Few persons of older age, however,are able to adjust to the use of contact lenses. This is especially trueas many older persons have trouble inserting and removing the contactson a daily basis from their eyes.

Also, correction of myopia through the use of various corneal implantswithin the body of the cornea have been suggested. Various designs forsuch implants include solid and split-ring shaped, circular flexiblebody members and other types of ring-shaped devices that are adjustable.These implants are inserted within the body of the cornea for changingthe shape of the cornea, thereby altering the its refractive power.Although these corneal implants attempt to correct for the myopiccondition, they do not adequately accommodate for presbyopia.

BRIEF SUMMARY OF THE INVENTION

The present invention is directed to a bio-compatible corneal implantfor correction of myopia and accommodation for presbyopia. The cornealimplant is ring-shaped and made from a bio-compatible material with alens body having an inner and outer circular edge. The inner circularedge forms an opening in the lens body. The posterior surface of thelens body has a uniform radii of curvature between the inner and outercircular edges. The anterior surface has two radii of curvatures. Thefirst radii of curvature extends from near the outer circular edge to ajunction point before the inner circular edge. The second radii ofcurvature extends from the junction point and continues to the innercircular edge. In one embodiment, an aspherical surface transitions thefirst radii to the second radii of curvature. This aspherical curvatureprovides a smooth transition between each radii of curvature whichreduces the thickness of the junction point. The inner and outercircular edges have a thickness less than about 0.020 mm and preferablyabout 0.010 mm.

The corneal implant, when placed under a lamellar dissection made in thecornea (such as a corneal flap), to relieve tension of Bowman'smembrane, alters the outer surface of the cornea to correct therefractive error of the eye. By relieving the pressure and subsequentimplantation of the device, the pressure points which typically aregenerated in present corneal surgeries are eliminated, and hence reducesrisk to patients of extrusion of implants. Unlike an implant placed inan intact cornea where corneal tissue can be deflected anteriorly orposteriorly leading to unpredictable refractive correction, properrelief of the pressure due to dissection of the Bowman's membraneensures that all the corneal changes take place at the anterior surface.

For the correction of myopia, the implant is shaped into a meniscus lenswith an anterior surface of the second radii of curvature being flatterthan the posterior surface. When the implant is placed concentrically onthe stromal bed the curvature of the anterior surface of the cornea inthe optic zone is flattened to the extent appropriate to achieve thedesired refractive correction.

For the accommodation of presbyopia, the corneal implant has a circularhole. When implanted on the stromal bed and the corneal flap ispositioned over the anterior surface of the corneal implant, a slightanterior oriented curvature is thereby retained in the center of thecornea leaving extra power needed for near vision, thus correcting forpresbyopia.

The material from which the corneal implants are made is preferably aclear, permeably, microporous hydrogel with a water content greater than40% up to approximately 90%. The refractive index should besubstantially identical to the refractive index of corneal tissue. Otherbio-compatible materials from which the corneal implant may be made,include: polymethlmethacrylate (PMMA), silicone polymers, UV-absorbingacrylic, hydrogel, microporous hydrogel, collamer, collagel acrylicpolymers, and other composite materials.

The refractive index of the implant material should be in the range of1.36-1.39, which is substantially similar to that of the cornea (1.376).This substantially similar refractive index prevents optical aberrationsdue to edge effects at the cornea-implant interface.

BRIEF DESCRIPTION OF THE DRAWINGS

A better understanding of the invention can be obtained from thedetailed description of exemplary embodiments set forth below, whenconsidered in conjunction with the appended drawings, in which:

FIG. 1 is a schematic illustration of a horizontal section of a humaneye;

FIG. 2 is a schematic illustration of an eye system showing adjustmentof the cornea to flatten the corneal slope to correct for myopia;

FIG. 3 is a 3-dimensional top view of one embodiment of the cornealimplant;

FIG. 4 is a 3-dimensional top view of another embodiment of the cornealimplant;

FIG. 5 is a 3-dimensional, cross-sectional top view of the cornealimplant;

FIG. 6 is a 3-dimensional, cross-sectional bottom view of the cornealimplant;

FIG. 7 is a cross-sectional top view of the corneal implant;

FIG. 8 a is a schematic illustrating a top view of the corneal implant;

FIG. 8 b is a schematic illustrating a cross-section of the cornealimplant shown in FIG. 8 a;

FIG. 9 a is a schematic illustrating a top view of the corneal implant;

FIG. 9 b is a schematic illustrating a cross-section of the cornealimplant shown in FIG. 9 a illustrating an aspherical blended surface;

FIG. 9 c is a blown-up view of part of FIG. 9 b illustrating anaspherical blended surface;

FIGS. 10 a and 10 b are schematic representations of a lamellardissectomy, with FIG. 10 b showing in particular the portion of thedissected cornea being connected through a hinge to the intact cornea;

FIG. 10 c is a schematic representations of a cornea in which thecorneal implant have been implanted lamellar for a myopic correction andaccommodation for presbyopia; and

FIG. 11 is a schematic illustrating the use of the corneal implant forcorrection of myopia and accommodation of presbyopia.

DETAILED DESCRIPTION OF THE INVENTION

Referring first to FIG. 1 of the drawings, a schematic representation ofthe globe of the eye 10 is shown, which resembles a sphere with ananterior bulged spherical portion 12 that represents the cornea. The eye10 is made up of three concentric coverings that enclose the varioustransparent media through which light must pass before reaching thelight sensitive retina 14.

The outer-most covering is a fibrous protective portion that includes aposterior layer which is white and opaque, called the sclera 16, whichis sometimes referred to as the white of the eye where it is visiblefrom the front. The anterior {fraction (1/6)}th of this outer layer isthe transparent cornea 12.

A middle covering is mainly vascular and nutritive in function and ismade up of the choroid 18, the ciliary 20 and the iris 22. The choroidgenerally functions to maintain the retina. The ciliary muscle 21 isinvolved in suspending the lens 24 and accommodating the lens. The iris22 is the most anterior portion of the middle covering of the eye and isarranged in a frontal plane. The iris is a thin circular disccorresponding to the diaphragm of a camera, and is perforated near itscenter by a circular aperture called the pupil 26. The size of the pupilvaries to regulate the amount of light that reaches the retina 14. Itcontracts also to accommodate, which serves to sharpen the focus bydiminishing spherical aberrations. The iris 22 divides the space betweenthe cornea 12 and the lens 24 into an anterior chamber 28 and posteriorchamber 30.

The inner-most covering is the retina 14, consisting of nerve elementswhich form the true receptive portion for visual impressions that aretransmitted to the brain. The vitreous 32 is a transparent gelatinousmass which fills the posterior {fraction (4/5)}ths the globe 10. Thevitreous supports the ciliary body 20 and the retina 14.

In the normal (emmetropic) eye, objects are properly focused on theretina. A number of factors determine how light rays are focused on theretina. Basically, these include the shape of the cornea, the power ofthe natural lens, and the length of the eye. The shape of the corneadetermines a fixed refractive power. If the cornea is too steeply curvedrelative to the length of the eye or if the eye is too long relative tothe curvature of the cornea, then myopia results. If the cornea is tooflat or the eye too short, then hyperopia results. In the normal eye,the shape of the natural lens can change thereby causing a change in therefractive power of the natural lens allowing the eye to change itsfocal point.

Referring to FIG. 2 of the drawings, the globe of an eye 10 is shown ashaving a cornea 12 with a normal curvature represented by a solid line34. For people with normal vision, when parallel rays of light 36 passthrough the corneal surface 34, they are refracted by the cornealsurfaces to converge eventually near the retina 14 (FIG. 1). The diagramof FIG. 2 discounts, for the purposes of this discussion, the refractiveeffect of the lens or other portions of the eye.

Typical of the myopic eye, the normal corneal curvature causes the lightrays 36 to focus at a point 44 in the vitreous which is short of theretinal surface. If the cornea is flattened as shown by dotted lines 46through the use of a properly-shaped corneal implant, light rays 36 willbe refracted at a smaller angle and converge at a more distant pointsuch as directly on the retina 14 as shown by dotted lines 48.

The above common refractive disorders of myopia and presbyopia aremeasured in units called diopters. Diopters represent the amount ofcorrection needed to normalize vision. Ordinarily a prescription iswritten in three numbers ±A±B×C. A identifies the degree ofnearsightedness or farsightedness. The plus sign indicatesfarsightedness and the minus sign indicates nearsightedness. Bidentifies the degree of astigmatism. C is the axis identifying thedegree of astigmatism. The more nearsighted, farsighted, or astigmatic aperson is, the higher the prescription will be in diopters.

The refractive correction needed for each individual is specific to thepersons shape of the eye and cornea. In selecting the proper dimensionsof the corneal implant for a patient the refractive correction formyopia and presbyopia must be determined. Generally, this includesdetermine the K-value or steepness of the cornea, what myopic correctionis needed, and what presbyopic add (power) is needed. These requirementsdetermine the size of the central hole.

FIGS. 3-7 illustrate the inventive corneal implant 50. The cornealimplant has an inside diameter 51, an optical zone 52, and an outsidediameter 53. The outside diameter and the inside diameter each have anedge thickness, 57 and 58 respectively. The inner and outer circularedges have a thickness of less than about 0.020 mm and preferably areabout 0.010 mm.

The anterior surface of the corneal implant has a first radii ofcurvature 55 and a second radii of curvature 54. The first radii ofcurvature 55 begins from the outside diameter 53 and continues to ajunction point 60 between the inside and outside diameters 51, 53. Thesecond radii of curvature 54 continues from the junction point 60 andextends to the inside diameter 51. The posterior radii of curvature 59extends from the outside diameter 53 to the inside diameter 51. Ajunction point 60 exists between the first radii of curvature 55 and thesecond radii of curvature 54. A junction thickness is defined betweenthe junction point 60 and the posterior radii of curvature.

The inner diameter is preferably between about 2 and 4 mm, although theinner diameter may exceed this range and may be configured in variousincrements according to the needs of the patient. Variation of the innerdiameter allows differing amounts of central power add to be achieved.The central cornea is centrally steeped which provides a central poweradd at the anterior cornea surface. Generally, the central power addprovides presbyopic correction up to about +4 diopters. However, agreater power add correction may be obtained.

FIGS. 8 a and 8 b further illustrate the inventive corneal implant. FIG.8 a is a schematic illustrating a top view of the corneal implant. FIG.8 b is a schematic illustrating a cross-section of the corneal implantshown in FIG. 8 a.

In one embodiment, an aspherical surface transitions the first radii tothe second radii of curvature. This aspherical curvature provides asmooth transition between each radii of curvature. FIGS. 9 a-9 b areschematics illustrating a blended aspherical surface 61 blending thefirst and second anterior radii of curvature. FIG. 9 b is a schematicillustrating a cross-section of the corneal implant shown in FIG. 9 aillustrating an aspherical blended surface. FIG. 9 c is a blown-up viewof part of FIG. 9 b illustrating an aspherical blended surface 61.

Table 1 is illustrative of various lens dimensions of the inventivecorneal implant 50 showing myopia correction ranging from about −1 toabout −12 diopters. Dimensions of the lens may be changed to achieveother myopic and presbyopic correction. Accordingly, the table is notmeant to limit the scope of dimensions of the corneal implant. For thetable below, the outside diameter 53 is 7.000 mm, the optical zone 52 is6.000 mm, the inside diameter 51 is 2.000 mm, the inner diameter edgethickness is 0.010 mm, the outer diameter edge thickness is 0.010 mm. Inthe table each radius and the junction thickness is represented in mm.TABLE 1 FIRST SECOND JUNCTION POSTERIOR RADIUS RADIUS DIOPTER THICKNESSRADIUS R1 R2 −1.00 0.013 7.000 6.855 7.135 −2.00 0.026 7.000 6.595 7.275−3.00 0.038 7.000 6.364 7.420 −4.00 0.051 7.000 6.157 7.571 −5.00 0.0637.000 5.971 7.729 −6.00 0.076 7.000 5.804 7.894 −7.00 0.088 7.000 5.6528.065 −8.00 0.101 7.000 5.514 8.244 −9.00 0.113 7.000 5.388 8.432 −10.000.126 7.000 5.272 8.628 −11.00 0.138 7.000 5.167 8.833 −12.00 0.1517.000 5.069 9.049

Table 2 further illustrates various lens dimensions of the inventivecorneal implant 50 showing myopia correction ranging from about −1 toabout −12 diopters. Dimensions of the lens may be changed to achieveother myopic and presbyopic correction. Accordingly, the table is notmeant to limit the scope of dimensions of the corneal implant. For thetable below, the outside diameter 53 is 6.000 mm, the optical zone 52 is5.500 mm, the inside diameter 51 is 4.000 mm, the inner diameter edgethickness is 0.010 mm, the outer diameter edge thickness is 0.010 mm. Inthe table each radius and the junction thickness is represented in mm.TABLE 2 FIRST SECOND JUNCTION POSTERIOR RADIUS RADIUS DIOPTER THICKNESSRADIUS R1 R2 −1.00 0.011 6.700 6.490 6.823 −2.00 0.021 6.700 6.047 6.951−3.00 0.032 6.700 5.683 7.084 −4.00 0.042 6.700 5.379 7.222 −5.00 0.0536.700 5.123 7.365 −6.00 0.063 6.700 4.905 7.514 −7.00 0.073 6.700 4.7187.670 −8.00 0.084 6.700 4.556 7.831 −9.00 0.094 6.700 4.415 8.000 −10.000.104 6.700 4.291 8.177 −11.00 0.114 6.700 4.182 8.361 −12.00 0.1256.700 4.085 8.554

The present corneal implant 50 can be implanted in the cornea using alamellar dissectomy shown schematically in FIGS. 10 a, 10 b. In thisprocedure, a keratome (not shown) is used in a known way to cut aportion of the outer surface of the cornea 12 along dotted lines 68 asshown in FIG. 10 a. This type of cut is used to form a corneal flap 70shown in FIG. 10 b, which remains attached to the cornea 12 through whatis called a hinge 72. The hinge 72 is useful for allowing the flap 70 tobe replaced with the same orientation as before the cut.

As is also known in the art, the flap is cut deeply enough to dissectthe Bowman's membrane portion of the cornea, such as in keratome surgeryor for subsequent removal of the tissue by laser or surgical removal. Acorneal flap of 100 to 200 microns, typically 160 to 200 microns, ismade to eliminate the Bowman's membrane tension (which minimizes cornealnerve damage). This helps to conform the flap to the lens surface,thereby transferring all of the change of the shape to the anteriorsurface of the cornea. This makes refractive correction more reliableand predictable. Also, the possibility of extrusion of the implants isreduced due to pressure generated within the cornea caused by theaddition of the implant. The corneal implant 50 is shown implanted inthe cornea in FIG. 10 c respectively, after the flap has been replacedin its normal position. These figures show the corrected shape for theouter surface of the cornea as a result of implants of the shapesdescribed.

FIG. 11 is a basic schematic illustrating the use of the corneal implantfor correction of myopia and accommodation of presbyopia. The lens 50 isshown implanted in the cornea 12. The corneal flap 70 is shownpositioned on the anterior surface of the corneal implant 50. Whenviewing distant objects, light rays 74 entering the cornea pass throughthe optical zone and inner diameter of the lens 50. Using the correctmyopic diopter correction, distant object become clear. The center ofthe object remains unfocused, but is not descernable by the eye.

When viewing near objects, such as text in a book, the eye utilizes thelight rays 73 entering through the center portion of the cornea. Asillustrated, the corneal flap 70 as laid over the corneal implant 50provides for a presbyopic diopter correction. Thus, the wearer of theimplant may focus on near objects, as well as distant objects.

Although one or more embodiments of the present invention has been shownor described, alternative embodiments will be apparent to those skilledin the art and are within the intended scope of the present invention.

1. A corneal implant for correcting myopia and accommodating forpresbyopia, said implant comprising: a lens body being made of opticallyclear bio-compatible material, the lens body having an anterior surfaceand a posterior surface and having an inner diameter edge and an outerdiameter edge, the inner diameter edge forming a central opening in thelens body; the posterior surface being curved in shape with a posteriorradii of curvature; and the anterior surface being curved in shape witha first anterior radii of curvature and a second anterior radii ofcurvature; wherein the diameter of the outer diameter edge is betweenabout 5 mm and about 7 mm and the diameter of the inner diameter edge isbetween about 2 mm and 4 mm.
 2. The corneal implant of claim 1, whereinthe posterior radii of curvature extends from the outer diameter edge tothe inner diameter edge.
 3. The corneal implant of claim 1, wherein thefirst anterior radii of curvature begins adjacent to the outer diameteredge and ends near a junction point, and the second radii of curvaturebegins from near the junction point and ends near the inner diameteredge.
 4. The corneal implant of claim 1, 2 or 3, wherein the firstanterior radii of curvature is less than the second anterior radii ofcurvature.
 5. The corneal implant of claim 1, wherein the inner diameteredge thickness is less than about 0.020 mm.
 6. The corneal implant ofclaim 1, wherein the inner diameter edge thickness is about 0.010 mm. 7.The corneal implant of claim 1, wherein the outer diameter edgethickness is less than about 0.020 mm.
 8. The corneal implant of claim1, wherein the outer diameter edge thickness is about 0.010 mm.
 9. Thecorneal implant of claim 1, wherein the inner diameter edge thicknessand the outer diameter edge thickness is less than about 0.020 mm. 10.The corneal implant of claim 1, wherein the inner diameter edgethickness and the outer diameter edge thickness is about 0.010 mm. 11.The corneal implant of claim 1, wherein the diameter of the outerdiameter edge is between about 5 mm and about 7 mm and the diameter ofthe inner diameter edge is between about 2 mm and about 4 mm.
 12. Thecorneal implant of claim 1, wherein the clear bio-compatible materialconsists essentially of any one of the group of hydrogel, microporoushydrogel, polymethyl methacrylate, silicone polymers, UV-absorbingacrylic, acrylic polymers, collamer, and collagel.
 13. The cornealimplant of claim 1, wherein the corneal implant is adapted for myopicdiopter correction ranging from about −1 to about −12 diopters.
 14. Thecorneal implant of claim 1, wherein the corneal implant is adapted forpresbyopic diopter correction ranging to about +4 diopters.
 15. Thecorneal implant of claim 1, wherein the bio-compatible material has arefractive index substantially identical to the refractive index ofcorneal tissue.
 16. The corneal implant of claim 1, wherein anaspherical surface transitions the first radii of curvature to thesecond radii of curvature, and the anterior surface of the second radiiof curvature being flatter than the posterior surface radii ofcurvature.